Selective call system



.Pune-*27, 1950 DEVAUX 2,512,613

\ SELECTIVE CALL SYSTEM Filed July 25, 1947 y 2 Sheets-Sheet 2 ESF L-:tld-

ASF

Nl2..5456789l0.

L- 1 T- b 1 ATTORNEY Patented June 27, 1950 i PATENT OFFICE 2,512,613 SEEECTIVE GALLiJsYs'rEM -Isienl' Devaux-Paris; France-assign@ ffp'mter- Y'-'I'atioml Standard Electi'ic- Corporation," New lYork, -N; SY., .afix'zt'rlperationl` o1 fDelaware Applicatirflulyiza iamjsriarisrn. "zs'sis :fIn'France September 1,1945

fSectionz1,1P1thlicLaw 690;August`f8;ii1946 P-atentfexpires- September1,-; 1965 s'f'cmims. `(CL-*edwin `Given'a group ofdradotelephonellstations, each consisting lof ai transmitter-and ia receiver, that have to :cmmuncatefwith ieahlothenthe bj ect of the; :present irventon.' ,is afnfaiparatus l to be asseated" toweahstatinfIor the` purpcsefot selectively,callinglanyfother stat'inv and ,conversing withA viti'Without11')osfsblit'y. :f interferentie Yfrom thevther stations. Sincefseveal `vconvesationshave fto be .exehangedsimultaneously. between .the'lvarou-sfstations lof the `go'im, it's 'necessary for c several wavelengths to befiiovided and -fr`.the.`reeiving andtransmittinglappratuses tob ef provided'` With dvies for the immediate adjustment 0f the wavelength, .thesewdevices being actuated, for example, byfmeans. ofpushfbttons lin av We1ll`k`nWn man-ner.

The 'present inventionfhas as tsbject the "reduc-tiontosa,zrninim'um"fy the operatins'necessary frfestablishinglan. itermliunicatn; and the ezireh'isive Juse ofmmbers of sa ,type lregularly .embly'ed inthefa'rtof telho'y. The description will be .conlufied" to that of the-le1ectr`c "diagram, sin'e .-selectrsfelajfs,.keyLswtches ,calling ldials, etc.; of. any typema'y} ."eoused-` inthe.v constructin.

Figs 111,:- andilb. fthed'rawing -appendedto the psetfdesrption whenfplacedsideby side' repitesentan` overall. schematic of .an ekample fof embodiment for association. w'itheraditelephone s'tatin consistingfof transmitter TRlandreceiver RE, Seach @provided vith -`adjusting (buttons for selecting the nplyd'inavelgth.

-Refei'ingjo Nthe drawing, the described example ffembodi'm'ent essentially eomr'ses .the

follwingfmembers;

RD cuts out microphone M and replaces it byw oscillator OSC in order to modulatethe wave transmitted by TR. A contact of RD'eXcites thev relay contained in transmittenTRin order to connect the transmitterl to the antenna and cut CF is not charged at the start, the currents are equal in :n and y, and RF is not energized because they act in opposite directions. It is even suitable for winding tobe preponderant, but for thediiference tobe insufficient to cause the at traction' o'fy the armature. The current diminishes in :l: in accordance with the charging of CF, and there arrives a moment when the out receiver RE, and RD also separates radi'oreceiver RE from the signal operating circuit in order to prevent a local action. RD will remain pulled up as far as position of SC.

Transmitter TR immediately-"sends a high? current in :c is too weak to sufficiently diminish the excitation produced by y, and RF operates. I tthen closes the circuit of ELT, over ILT, LTb2 and operating contact of RF. LT passes into position 3 and thecurrent is cut off in x and y.

. CF then discharges into the two windings a: and

y. in series, and RF remains pulled up for a long moment. When it falls back, its rest contact closes the circuit of ELT over ILT and LTb3. LT

frequency Wave modulated at the low frequency of oscillator OSC. This wave is received by all the stations that have button I of the receiver depressed; it serves first of allV for marking the occupation of the calling frequency. As will be explained further on, this results in the operation of the RA relays, andv then of the RB relays, in all the stations, and the busy lamp I il is lighted' in all the stations. Furthermore, thecircuitof RC is broken,` lsothat no other station can make a'call. 'l

At .position 5.0i SC, the circuit'of ESCis closed over: I SCE, SCGLCA@ and rest fcontact ofz RD. ESC pulls'up its "armaturavand this opens ISC, but ESC remains energized 4across resistance RSC, so that SC "remains at position 5. l

The return of the dial effects four .interruptions of the modulation and, at the end of the movement, contact CAa Opens; ESC releases and SC passes intoposition 6.

The operator vsends the units digit 5 insimilar manner and, at thenflnish,` SCMpasses into position 7. The operator` .similarly sends ,the number of the frequency 7fthat he has found to befree, and SC'passesinto lposition 8, but SC cannot remain at` `DOSition 8', .since the. circuit of ESC is closedover ISCa and SCb froma to` l5. SC. arrivesat position 1l. Where itbreaks thecircuit of RC whichreleases andv again closes the circuit of ESCv over I SCcl and SCa and the rest contacts of lRC` and RB. SC returns to posi-v tion1 ..r. .k l Upon reaching4 position 11, SC no longer closes the circuitof RD which releases.slow1ybeing retarded by condenser CD, so` that the, modulafA tion still continues, e. g. foronesecond.

After having thus, sent the number .of .the Wanted station and indicated the conversation frequency to be employed, the calling operator presses down buttons] vof, ,the transmitter and the receiver, and listens in for an answer from the called station. ,Y f It is necessary to preventa negligient operator from v,blocking the calling frequency ,by sending anv incomplete. call. .The time. at his disposal for sendingthe ldigits is. accordingly limited by. thetime umiteselector- L11?. As soon as SC reaches position 5, .the circuit of AELT is closed over ILT, LTaI and SCd5. .LT immediately passes into position 2', and it begins to lmeter the .time byvsetting retardation relay RF into operation,.as will be describedfurther on.y y

kRF is a differential relaywhich has one of its windings a: in series with `a high capacity condenser CF. When LT reaches position 2, it simultaneouslycloses thecircuits o f.the two winding :z: andy y across LTc2.I Since condenser Apasses into? 'position 4 Where it again closes the circuit of :c and y.

VThe same operations` are repeated, and LT passes slowly to the next positions as far as position 11 which it reachesin a' time that is dependent on resistanceslr and gland on Athe capacitance of CF. This time maybe fixed at l5 or 20 secends, for example.

At position 11 of LT, the 'circuit of ARSC is closed over ISC, SCIJS,l Sor 'I depending upon the position at which the operator has stopped, and LTcI I. SC` immediately passes into positions and from there returns to position l, ias already explained, thus stopping the emission of modulated current.

If the operator hasv completed the'call before LT reaches 11, SC will haveI arrived at 1 and vit brings back LT to l'by closing the circuit of ELT over ILT, LTa2 to 1l andSCaI. Similarly, LT passes fromlposition l; to position 'l WhenSC arrives at 1 after having been brought'back there by LT. ,y I

The Yoperation at the other stationswill now be described. The Wave modulated at the calling frequency isreceived by all the stations that have their receivers No. I buttonpressed down.

The radiorecefiver delivers the modulation frequency to the signal receiving circuit. This Wave isselectedby a resonant circuit CR in series with a high Aresistance RR; it amplied by afirst tubeLAI detected bye. tube ID, and the rectified voltage is applied to a pentode polarized below the cutroff point LA2 from which the plate circuit passes overrelay RA. y This relay operates immediately and'closes the circuit 0f relay RB which operates without delay but, which is shunted by a'high capacity condenser CB for the purpose of making it slow to release, so that it remainspulled up during the interruptions of the modulation; RB closes the circuit of the busy lamp LO, and this indicates to all ,the stations that a call is in progress. Furthermore, RB breaks the circuit of contact CALL, sothat if an operator of any station tried to make a ,call despitethe indication of thebusylarnp, he vcould not do so because relay RC would. not operate. RB closes the cir-v cuit of ESC over ISCa yand SCdI, and sequence sWitchSC passes into position 2 in all the stations in receiving position. y

Upon ,the sending of the first digit, relay RA of all the vstations in receiving position falls back at each interruption of the rnodulation.v SC closes the circuit of ESD overl ISD, RE, contact of RB and rest contact ofv RA. ESDpulls up its armature. RE is shunted by a dry rectier RS which does not retardV they relay Whenpulling up,.but retards it when releasing. RE closes the circuit of ESC over ISCb, SCcZ ,andcyontact of RE. ESC pullsl up its 'armature',`and thisopens contact ISCb, but theattraction persistsbecause theroircuitzotESC remains closed .across resistance RSC,

so that :the selector does not rotate.

After the firstinterruption, when themodula-'l' ing the interyalbetween two iinterruptionsfof the modulation.

."ll'he second interruption of ithe .modulation causesSD :to pass intoposition2,and so on asfar as :position 4.

'.Ilhe ,callingeperator then lsends theidigit A ,suiiicient time interval elapses .between the" sending of the digit 4 and that of the next digit 5" forL-RE to release, .and this vopens :the circuit fof ESC; TSC passes into Aposition r3.

'fInnthis 4.position of .SC,-ESD is vout-out andfisv replaced rby ESU. Thei5 interruptions oithecall-v ing dial cause SU .to pass into -position=5, and RE is again in zthe operating position. At :the nishof .the train of interruptions, RE falls back and causes l SC to pass into :position 4.

'.Ilhe ycalling yoperator then xsends the number of theffrequency he has found tobe free, i. e. 7.

lSelectors SD and SU .of -all lthe v*stations have accordingly :been brought to positions 4 and`f5 respectively, ibut :only :the station 4:bearing No. 45 has a connection (indicated in dotted lines) `loetween contact 4 of ban-k :b vofxfSDand c0ntact`5 of bank bof SU. Thisconnection servesfor 'closing :the lcircuit .betweenthe rest contactofRAand ESF, so that .only selector'SFof station 45 will rotate for ythe interruptions sent. SF, upon leayingithenormalzposition N, accordinglyreaches position '7. j

.fAs soon 'as SFleaves position N, it closesthe circuitoi bell S 1to-contact bank fb; station 45' isaccordingly rung.

Selector SF carries .a numbered fdrum which dicate tothe operator of .the .called statiozrthe versation.

yUpon terminationfof vthe sending of thenuniber of "the frequency to be employed, SC passes into position 5 through :the falling back-of the :armature ofRA.

soon as the three digits that make upthe call sign have fbeen sent, andSC of the called station'has reached position 5, the circuit of'cELT is 1closed kover LTI :and SCd. LT 'begins to rotate, as already explained-and it meters the :time so that if the opera-torni the called-stationidoes not answer, the apparatuses will be brought .back to the resting position at the end of a certain time, as already explained.

The .operator of the lcalled station notes-the num-ber of the conversation frequency, tlinthe selected example; he presses down `buttons i of the transmitter and the receiver, answers Yand stops the ringing by momentarily depressing but ton BS,'thus closing-the circuit of cESC over =ISGa, SCbE to vl, and the-buttomscontact. SC--imme diately passes into position 8,andffrom there into position l-l, and when lthe 4transmission Vof 'the modulation stops, `RIB -falls 4hack -a --moment later and SC returns tc position l, as already Aerplained.

`At position `l, SC closes'the-circuit of ELT over ILT, 'LTaZ toll and--SCc-i. LTreturnsito-position 1 in which it closes the -circuit of ESD over ISD, SDal vto il, L'Tl andSCci. vSD returns to its normal position in which it closes the circuit of ESD over ISD, SDaI to il, LTaI and SCcl. SD

asians '1 appears behind Ya :window -oftheapparatus to inv returnsto its normalposition Airr which it closes the circuit `of ESUoyer ISU, SUa I :to andfSDN.

SU returns to -it's normal "position `inwhichfin its turn, it .closes the @circuit .of `ESF A,over ISR SFaI tion-:the vringing circuit is cutout, andalletheapf paratuses return to the resting position.

-Incase cino answer, LT reaches position 11 in which-it@closes-the circuit of ESC over ISCcS to 8. plained, .and it ithen successivelylbrings theother selectors tothe-.resting position. l.

In the stations that have notfloeen called,SC has :remainedrat .position 4. .A moment after, the

transmission cf Ytheinodulated wave has '.ceased; RiB yreleases andr closes the circuit of ESC overl lSCa, SCad .andthe restcontacts of RC and f-RB..

SCpasses .into position 5 .in which the fcircui-tpf ESC .is closed ,over ISCa, SCM, SFbN, :andthe rest contacts of RC vand RB. SC. `passes intogposi-4 tioni and ,from there fit-returnstoposition lainy which it brings SD andSU to the resting position,

as .already-explained. j.; 'Upon termination of the conversation, the only manipulation the yoperators have to make is that of pressing Adown the adjustment keys vof the. transmitter and .ithefreceiver to 'the frequency gl, i so-that the stations may bein position to receive acall.'

The .system is `applicable to the simultaneous calling ofa1l.the stations or ,of a group ofgsta' tions. For example, the drawings show the ar,-

rangement `that serves for calling all :the sta.

tionsby-.meanso the call sign 00. It sufiioient to make a direct connection between ,SDbU and SUM). FBysending zero twice, the two selectors SD.V and SUcf all thestations are 'brouglitfto the -v position 0 and the circuit of SF is closed toall the stations, Aso 'that the third digit indicatingithe conversation frequency is received fby all thestax tions on .selector GSF. Other numbers mayibere.- servedior'gwupsof stations.

- A -nurnfloersoiV apparatuses in-,excess ioiyonerhunrality vci different frequencies, `means ateach station forselecting an idle one of said frequencies'for communication, anormally inactivesta'-v v;

tion-selector at each vstation for determiningfthe selection of itsstation, means including a-rst relay Aat each--station vfor controlling the connestion' for operationof the transmitter and receiver thereof, vandi-or controlling the operation of at station selector in aca-lledstation, a'second relay at -each station, inea-ns 4ior-operatimg the second relay 4at* each 'station Avwhose receiver responds 4to a frequency selected andtransmittedebythecallingsta-tion, means controlled by the operatedsecond' relay `for controlling v the associated circuit of the'rst relay -o-f lthe same station to preventthe initiation-of a call from astation'whosefreceiver has responded, a multi-position switch atfeachl station, means 'for-moving the switchgatthe call-V ingstaticn `from position to` position in 4response tothe-operation lof a controlfor a station selector,v

means including a time limiter at each station for SC returns to position "l, as'a-lreadyveX-f- 7, limiting'y the time during which the operation of a station selector may be controlled at the calling station, means controlled by the time limiter for returning the multi-position switch to normal of stations, a variably tunable radio receiver and transmitter at each station, the receiver being normally active and the transmitter normally inactive, means including contacts for rendering the transmitter active during signaling and conversation, a microphone and an oscillator for each transmitter, electrical potential sources of a plurality of different frequencies, means at each station for selecting an idle one or said frequencies for conversation and a predetermined one of the frequencies for signaling, a normally inactive calling dial 'at each station, a normally inactive multi-position sequence switch at each station, means for moving the sequence switch into its first operating position responsive to the loperation of the associated dial at the same station, a first relay at each station having an energizing circuit closed by the sequence switch from the first to the last position thereof for controlling said contacts and for disconnecting the microphone of the associated transmitter, and connecting in its place the oscillator, and also for disconnecting the receiver, a quick acting second anda slow acting third relay iat each station, means for operating the second and third relays at each station Whose receiver responds to a frequency selected and transmitted by the calling station, a busy lamp responded, and means for moving the sequence switch at the calling station from position-toposition in response to the operation of the dial in accordance with successive digits designating the called station and finally the digit designating the frequency selected at the calling station.

4. The system according to claim 3, means including at each station a time limiter for limiting the time during which digits may be sent from the calling station and the called station may be signalled, a circuit controlled by the time limiter for returning the sequence switch of the calling station to normal position if within a predetermined length of time it does not pass through the digit sending positions, means controlled by the sequence switch for returning the associated time limiter to normal if digit sending is completed within a predetermined period, and an answering key at each station for moving the sequence switch thereat into normal position from an operating position.

5. The system :according to claim 4, and a differential retardation relay operatively associated with each time limiter cooperating in the control of the associated time limiter and sequence switch.

6. The system according to claim 3, a circuit for moving the sequence switch into second posiplurality of multi-position digit switches at each station, and circuits controlled by the sequence switches at the last mentioned stations for moving the digit swit-ches into positions determined by the quick acting second relay which responds to each digit pulse.

7. vThe system according to claim 6, a normally inactive multi-position frequency indicator at each station, a circuit for operating the frequency indicator only :at the called station, said circuit being jointly controlled by the digit switches and the second and third relays of the called station, and a signal at each station operated in all ofi'- normalvpositions of the frequency selector-'of that station.

8. The system according to claim 7, circuits for returning to normal positions the digit switches and frequency indicator at the called station when the sequence switch at the called station is returned to normal, and circuits for returning to normal the operated digit switches `at other stations than the called one jointly controlled by the third relay and sequence switch thereat.

9. In a telephone exchange system, a plurality of stations, a variably tunable radio receiver and transmitter for each station, means for rendering the transmitter active during signalling and conversation, electrical potential sources of a plurality of different frequencies, means at each station for selecting an idle one of said frequencies for communication, a normally inactive station selector at each station for determining the selection of its station, means including a lirst relay at each station for controlling the connection for operation of the transmitter and receiver thereof, and for controlling the operation of a station selector in a called station, a second relay at each station, means for operating the second relay at each station whose receiver responds to a frequency selected and transmitted by the calling station, means controlled by the operated second relay for controlling the associated circuit of the first relay of the same station to prevent the initiation of a call from a station whose ref ceiver has responded, a plurality of multi-position digit switches at each station, means controlled by the second relay at each called station for moving the digit switches in the positions determined by the station selector control at the calling station, a normally inactive multi-position frequency indicator at each station, and means controlled by the digit switches for operating the frequency indicator only at the called station selected by the station selector control.

LUCIEN DEVAUX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Y Name Date 1,608,551 Demarest et al Nov. 30, 1926 2,061,699 Fox Nov. 24, 1936 2,064,894 Espenschied Dec. 22, 1936 2,064,961 Tidd Dec. 22, 1936 2,101,668 Bishop et al Dec. 7, 1937 2,137,023 Monk Nov. 15, 1938 2,176,868 Boswau Oct. 24, 1939 2,226,692 Brunner Dec. 31, 1940' 2,265,056 Bowers Dec. 2, 1941 2,363,583 Gilman Nov. 28, 1944 2,383,908 Bowers Aug. 28, 1945 

